On habitability around red dwarf stars

Back in 2001 an interesting paper called red, willing and able was published on the ability for planets around red dwarf stars to have life. It was assumed for quite some time that in order for a planet around a red dwarf star to have a balmy climate it would have to have an atmosphere so thick that it would block out the light necessary for photosynthesis in the first place...but later simulations revealed that an atmosphere wouldn't need to be as thick as first assumed and thus the argument against planets around red dwarfs vanished.

Naturally, a planet in a habitable zone around a red dwarf star would be quite different from ours especially since it's likely to be tidally locked, with the same side facing towards its star all the time, giving it 24 hours of day on one side and 24 hours of night on the other, with a thin area in the middle where it would have a bit of both. However, an atmosphere would still be able to keep the temperature around the planet quite stable and thus it wouldn't necessarily be a hot desert on one side and a ball of ice on the other; just take a look at Venus for an example of how this works. Venus rotates so slowly it takes over 200 days just to turn once but the difference in temperature between the day and night side is almost nothing.

Add to this the extremely long lifespan of red dwarfs (and assuming it's not a flaring star like Proxima Centauri) and you have a remarkably stable platform for life to grow and develop. This is the background behind today's article on space.com about the subject, dealing specifically with how red dwarfs become more and more stable over time, and that planets that are able to hold on to an atmosphere during the first billion years should become pretty good candidates for life later on. It begins with this:

Roughly three quarters of the stars in the galaxy are red dwarfs, but planet searches have typically passed over these tiny faint stars because they were thought to be unfriendly to potential life forms.

But this prejudice has softened lately. Preliminary results from a dedicated research program have shown that planets around red dwarfs could be habitable if they can maintain a magnetic field for a few billion years.

and then gets into more detail. The article is actually a bit short but at the moment there are 35 comments, which are generally more interesting than the articles themselves. Now that Kepler is about ready to begin its mission we're getting very close to a huge treasure trove of new planets around red dwarfs, so we'll know a lot more about planets around them soon enough.

And while we wait there's also a page on Wikipedia about the subject too.


Edit: damn! One poster just made a really good point when discussing whether tidal locking would be a problem or not re: habitability of a planet:

I take the point about tidal locking, but I have never heard any comment on the possibility of a habitable moon of a planet orbiting a red dwarf. The moon would likely be tidally locked to the planet, not the star, wouldn't it, and would therefore rotate relative to the star. How come nobody ever discusses this case?